Localization in diphtheria toxin fragment B of a region that induces pore formation in planar lipid bilayers at low pH.

Like diphtheria toxin and the N-terminal (Mr 23 000) region of fragment B, CB1 (Mr 13 000), the cyanogen bromide peptide located in the middle region of fragment B is able to induce pore formation in lipid bilayer membrane at low pH. These two peptides (Mr 23 000 and 13 000) share a common segment (Mr 6300) containing the predicted amphipathic, alpha-helical, transverse lipid-associating domain (Mr 2750) of fragment B [J. Cell Biol. (1980) 87, 837-840]. Therefore, we postulated this domain to be responsible for the pore formation ability of diphtheria toxin [Proc. Natl. Acad. Sci. USA (1981) 78, 172-176]. A relationship between the pH dependency of pore formation and the presence of a cluster of prolines in the C-terminal region of CB1 is proposed.